1. Field of the Invention
The invention relates to difunctional, low molecular weight polyisobutylene polymers bearing terminal functional groups, their method of preparation and use in the synthesis of block copolymers.
2. Brief Description of the Prior Art
Kennedy describes in U.S. Pat. No. 4,316,973 a class of telechelic polymers of the general formula: ##STR3## wherein PIB is a divalent polyisobutylene moiety and Y represents one of the monovalent groups of the formulae: ##STR4## These polymers have been found useful as soft segment components of certain block copolymers. For example, the U.S. Pat. No. 4,276,394 issued to Kennedy et al. describes the halogenated species as being usefully incorporated into a polystyrene elastomer. Also, Wondraczek and Kennedy described the synthesis of nylon-polyisobutylene-nylon triblock copolymers employing the hydroxyl-terminated polyisobutylene species; see Polymer Bulletin 2, 675-682 (1980) published by Springer-Verlag. The same hydroxyl-terminated species was incorporated into a block copolymer of polyisobutylene and polycarbonate; see Liao and Kennedy, Polymer Bulletin 7, pp. 233-240 (1982).
The polyisobutylene polymers of the present invention are distinguishable from the prior art polymers described above and possess advantageous physical properties, such as a higher degree of thermal stability, not associated with the prior art materials.
Baldwin, in U.S. Pat. No. 3,392,154 described the desirability of obtaining relatively low molecular weight, carboxy-terminated difunctional polymers of polyisobutylene. However, the process described, ozonolysis of a butyl rubber followed by oxidation or reduction of the product of ozonolysis, apparently did not result in a difunctional, carboxy-terminated polymer as would be evidenced by a curable mastic. As stated by Baldwin, "it is difficult to approach the objective of two functional groups per polymer molecule by the process of the invention when the unsaturation in the chain is not of type II". A type II copolymer is not inclusive of isobutylene-isoprene copolymer (butyl rubber).
By the method of the present invention, poly(isobutylene co-isoprene) or poly(isobutylene-co-butadiene) is oxidized to obtain carboxy-terminated, difunctional polymers, useful in a wide variety of applications.